«Hitomegauti» - it's when they go to mourn for a dead person and fell heads of all of his relatives by the edge of a sword, and those who are minced beat in answer, and how many them much were, mince all the relatives, and if there is nobody alive then another clan mince instead of those who were minced and then choped wounds heal fast.

Hitomegauti "one hit striking" is when they hang a dead corpse [of an enemy] then they cut down heads of all of his relatives by the edge of a sword, and then those who are cut beat in answer, and how many them were, kill all the relatives, and if there is nobody alive then another clan cuts instead of those who were cut, and then cut wounds heal fast.

Well, although I’m not quite sure about the precise meaning of the original sentence, your translation sounds somewhat differs from the original, I’m afraid.
1. I’m not sure why you see the corpse is of an enemy.
2. This might be my misunderstanding. But "they cut down heads" doesn’t sound right to me. It reads that they "hit" one another with the sword. They did not "kill" them although it says somebody sometimes ended up "almost dead" in the ceremony.

To me, this odd ceremony seems to have intended to perform an exorcism or something when someone died in the community. But I might be totally wrong. Just my two cents.

Question: Why is Katakana used where we would use Hiragana today? My understanding was that Japanese originally used only Chinese Characters, and that Hiragana was a feminine script. But if Kana was to be used, I still would have expected Hiragana rather than Katakana

Question: Why is Katakana used where we would use Hiragana today? My understanding was that Japanese originally used only Chinese Characters, and that Hiragana was a feminine script. But if Kana was to be used, I still would have expected Hiragana rather than Katakana